1. Field of the Invention
The present invention relates to semiconductor laser devices and more particularly, to a semiconductor laser device having a stripe-like current path and a manufacturing method thereof.
2. Description of the Background Art
Conventionally, AlGaInP semiconductor laser devices have been intensively studied and developed as semiconductor laser devices having lasing wavelength in the red band. The AlGaInP semiconductor laser devices are capable of lasing light in the band of 630 to 680 nm. Since this wavelength band has high visual sensitivity, such semiconductor laser devices are used as laser pointers, line markers, etc. Furthermore, they are expected to be used as light sources in high density recording systems, etc., because of their shorter lasing wavelength as compared with AlGaAs semiconductor laser devices.
Such semiconductor laser devices generally use a GaAs layer as a current blocking layer. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL.1, NO.2, JUNE 1995, pp.723-727 shows an example of a ridge-type semiconductor laser device which adopts a double-layer structure including an AlInP layer (an optical confinement layer) and a GaAs layer as a current blocking layer.
This reference discloses that the semiconductor laser device having the current blocking layer of double-layer structure improves a lasing threshold current and slope efficiency (the slope of current versus light output power characteristic in a lasing state) as compared with common semiconductor laser devices having a current blocking layer of a single-layer structure of a GaAs layer.
In the process of manufacturing such a ridge-type semiconductor laser device, generally, a stripe-like mask film of a dielectric material, such as an SiO.sub.2 film, is formed in the center on a semiconductor layer formed on a semiconductor substrate and the semiconductor layer is etched through the mask film to form a ridge. Then with the mask film left, a current blocking layer is formed on the flat areas on both sides of the ridge and side surfaces of the ridge by vapor-phase growth such as metal organic chemical vapor deposition (MOCVD)
However, when growing a current blocking layer formed of a material with a high Al composition ratio such as an AlInP layer without introducing corrosive gas such as HCl, which is undesirable for the manufacturing device, the high Al composition ratio material is formed like dots on the mask film of dielectric material even if growth conditions are selected. Consequently, when a current blocking layer composed of a GaAs layer is grown next, the GaAs layer, which usually does not grow on a dielectric material, is formed in a large area on the mask film with the high Al composition ratio material formed like dots as cores. It is then difficult to remove the mask film by wet etching or dry etching using reactive gas after the formation of the current blocking layer. As a result, part of the mask film remains in the finished semiconductor laser device, thus introducing the problem of low yield of devices.
On the other hand, further improvement of lasing threshold current and slope efficiency are generally required for semiconductor devices, not only for the AlGaInP semiconductor laser devices.
Particularly, the AlGaInP semiconductor laser devices have inferior characteristics of lasing threshold current and slope efficiency due to problems inherent in the material as compared with AlGaAs semiconductor laser devices and therefore there is a demand for further improvement of the characteristics.